Replacing a Leaking Bathroom Sink Drain

Here's my step by step on how I worked on replacing a leaking bathroom sink drain on our narrowboat. It includes cleaning up old silicone, lining up a slotted basin waste for an overflow, then sealing with Plumber's Mait.

AD | This sink repair is sponsored by WD-40®, which I have been using for several fixes and maintenance jobs throughout our recently purchased second-hand narrowboat renovation.

It's been all fun and games with the plumbing on our narrowboat since buying it. There's nothing wrong with our new boat as such, but in the first few weeks we've been getting things up to scratch such as fixing leaking waste pipes and changing a leaking mixer tap.

BUT, I then got obsessive checking other areas, and may have disturbed the sink's plumbing, as we then had a leaking sink drain.

So, let's explore it.

What We'll Cover While Repairing a Leaking Bathroom Sink Drain

In short, everyone's sink basin waste is likely to be installed differently. That's because plumbers or DIYers tend to have different methods when it comes to sealing a kitchen sink drain and the like.

During my leaking bathroom sink drain repair, I'll be talking about:

• Disconnecting a bottle trap from under a vessel sink on a narrowboat
• Removing a bathroom sink drain
• Helping you decide whether you should clean a sink drain, or replace it
• Removing old, dry Plumber's Mait
• Removing set silicone (and lots of it)
• What happens if you don't install a slotted basin when your sink has an overflow (it's gross!)
• Lining up a slotted waste basin
• Sealing a sink drain, but with Plumber's Mait
• Plumbing a bathroom sink drain
• Gluing the vessel sink back down

Plumber's Mait or Silicone?

Throughout learning how to fix a leaking basin waste, the main question I came across was "Should I use Plumbers Mait or silicone to seal it?" During this video, I found James' debate at Plumberparts really useful: How to Change a Basin Waste.

As usual, the internet is armed full of contradictory viewpoints. Some plumbers think silicone is more reliable. Others prefer a non-setting putty, such as Plumbers Mait.

Either way, from this experience, so far, I prefer Plumber's Mait because:

• I hate silicone as it often turns into a sticky mess
• There's no waiting for it to set, and you can test it immediately
•  It'seasy to store in a tub
• It's flexible, and I believe that once silicone loses contact with, say a sink, it will immediately start leaking

Paul the Plumber's Silicone Tip

My narrowboat neighbour, who is also a plumber, actually swears by silicone, and claims that Plumber's Mate can sometimes turn rock solid. So, if your bathroom sink drain is leaking and you prefer to use silicone, he suggests:

Adding a thin bead ring shape of silicone around the basin waste before the washer goes on, followed by the nut - which should do the trick. This also applies to a leaking kitchen sink drain.

Our Leak Under the Bathroom Sink Drain

Here's a photo (above) of the leaking plumbing under our bathroom sink.

Our vessel sink is mounted above a butcher's block-style wooden worktop. This also means our sink is glued down from above so I only had a small hole to work with to get to the plumbing.

As the basin wasn't glued down very well, possibly from wear and tear, it made sense for me to disconnect, remove and take it to a more spacious area on the narrowboat. That is, the dinette table!

Draining the Waste Water

It's a good idea to completely turn off the sink's water supply, either at your isolation taps or, your narrowboat water pump. Make sure you have a bucket and towel ready before you unscrew the bottle or p-trap, to catch drips underneath.

Asides from pouring the wastewater down the toilet, as an extra precaution, I thought I should also tilt the sink over the toilet.  I had the pleasure of discovering lots of yucky black sludge pour out of the overflow hole. By this point, I suspected this basin's waste didn't have any slots for it to escape.

My personal opinion is that, because boats get condensation build-up, you should always install a slotted drain.

Unscrewing the Basin Waste Nut

Here, you can see I've removed the narrowboat basin away from the bathroom, and it is now upside down. I'd already unscrewed the leaking pop-up drain cover from the top, then poked a knife in, to keep it still while unscrewing the large nut with water pliers.

After getting so far, I was able to unscrew the entire thing off by hand. Then push it out to discover that it indeed was an unslotted drain. So the overflow water had nowhere to go.

I had originally planned on simply cleaning this bathroom sink drain and reusing it. But due to the above, I needed to change direction, and replace a bathroom sink drain instead. I understand, I could have drilled a hole in it, but there was a lot of silicone around. So, for the sake of a tenner, I replaced it with a new one.

Fix Leaking Bathroom Sink Drain Steps

Cleaning Plumber's Mait with WD-40

This year, I've teamed up with WD-40®! I have found their Flexible Straw Penetrant Spray incredibly useful to have to hand during this leaking sink basin repair.

As soon as I finished removing the sink drain, I uncovered some fossilized plumber's putty.

So, to avoid scratching the sink's porcelain, I squirted with WD40® to lubricate it, and cleaned it all off with a green plastic scourer.

Tips For Removing Non-Set Plumber's Mait

If you need to remove sticky Plumber's Mait, then a squirt of WD40® should work too.

This also applies to unset PM around the screw area of the basin's waste - I have seen people using it with an old toothbrush, which works wonders.

Finally, give everything a final thorough clean with soapy water or solvent cleaning wipes, so no oil can interfere with future sealing of putty or silicone.

Removing the Basin's Washer or Gasket

Another issue I had, was the drain's rubber washer (or gasket) felt like it was welded onto the silicone.

So, again, I found myself reaching for WD-40® to spray around it in hope that it would come off easily.

This worked immediately!

Removing Old Silicone From a Sink

The next job I had to do was clean off the old silicone. Unfortunately, this part is what took me so long to get this job done, otherwise, it should have taken about 20 minutes.

In the above photo, I removed most of the thick gloopy excess silicone with a dull Stanley knife. I recommend doing this slowly and very carefully to prevent cutting yourself and possibly scratching your sink.

It was important that I removed it from the rim too, as it had been coming away. That way, when I reapply fresh silicone, it would be sound when in contact with the bathroom counter top.

Removing The Sealant Residue

With the silicone being pretty much everywhere, I'd previously bought some silicone remover. However, if you want to remove it with WD-40, I've since watched The Ultimate Handyman say here in his description, that it works just as well, if not better.

To remove the remaining sealant, I applied with a brush and left it for 15 minutes before scrubbing off. However, I needed to repeat again, and give a final clean.

This is where solvent wipes would be a good idea to ensure the silicone or putty seals properly.

Cleaning Washers With WD40®

When installing the new basin waste, I wanted to find the right washer for my sink. My basin's hole felt slightly chamfered, and I could have either used solely Plumber's Mait or a washer.

I found the original waste's washer was still the best fit, so I cleaned it up with WD-40® again, which also removed any water that may have still been on it.

After cleaning, you can see below that I slotted it on and didn't use plumber's putty here at all.

Other Options

During my research travels, I also found a Basin Mate without silicone or putty, which you might prefer. Or, something like a McApline slotted centre-pin basin waste. However, I didn't opt for these, due to mixed reviews.

Lining Up the Overflow Holes With The Slotted Basin Waste

We've already seen some black sludge which had been trapped in the sink. So, I made my best effort to line up the sink's two overflow holes with a new slotted drain.

Note, with the plug being twisty, I had no way to trap it with a knife to line up while I screwed, so here's what I did:

• Marked it with a pencil where the bowl's overflow holes were
• Added sticky foam on the chrome basin waste for reference where the holes were
• Placed the basin waste in the hole, and trapped it as best as I could with several strips of masking tape
• I could then flip it over, without it falling out

Applying Plumber's Mait

The next job was to seal my basin waste with Plumber's Mait putty from underneath.

After grabbing some out of the pot (and apparently, the more the better), I rolled some in my hands into a thick sausage.

Then, while propping up the drain as much as possible, I placed and gently pressed it around, making sure there were no gaps before threading a large polymer washer on top.

Sealing the Basin Waste

Once the large washer was on top, it gave me a larger surface area to trap the PM underneath and create a better seal than before.

I pressed it down firmly and evenly, then scraped off any excess that poked through the centre with a knife.

Next, I hand screwed the basin waste's nut on, while at the same time, holding and pressing the waste down from the other side to avoid twisting. Remember, I wanted to ensure the overflow holes would still align with the slots.

Tightening the Basin Waste Nut

I'd heard some horror stories about people tightening their nut to the point of cracking the sink or washer.

It was recommended to me that once I'd got it hand tight, that I should give it one full, final turn with water pliers.

Then, I should remove any excess putty again with a knife and put it back in the pot as it can be reused at a later date.

Plumbing The Sink Drain

Once I was happy with the new basin waste that I fitted, ensured that it lined up correctly with the overflow holes, it was time to take it back to the narrowboat bathroom. AKA, "The Head".

But something I learned with my setup is, that with the McAlpine being 40mm and the basin being smaller, ours had an adapter to screw onto the basin first.

The problem was, it got stuck so I needed to use WD-40® Specialist High Performance Silicone Lubricant Spray to separate them. I couldn't just screw the entire thing on as it was, as I'd lose control as to which way my waste outlet would aim.

Screwing the Bottle Trap To the Basin Waste

Now, my problem didn't end here. By the time I connected the bottle trap and turned the water back on and tested for drip, I had a new problem. And that was a drip from one of the McAlpine compressions.

This meant I needed to disconnect the trap AGAIN. So made the decision to replace it entirely with a new one, but the exact same part. *I later separated the old one to find a kinked washer and in all honestly, didn't want to waste more time checking for drips.

New traps are only about £10, which, for getting all hands on myself, I still saved money by not hiring a plumber to do my repairs.  Plus I learned something new in case I ever needed to fix a drip in the future.

The new waste had no problems whatsoever.

Gluing the Vessel Sink Down

After leaving some blue tissue under my trap for a few days to check for leaks, I knew it was safe to now glue the sink down.

To keep the mess to a minimum, I placed the sink where I wanted it, ensuring there was enough finger space to the drain from underneath.

I then masking taped around the sink for reference, AND to catch any silicone mess. Next, I propped it up while applying clear construction adhesive. I was going to use clear sanitary bathroom silicone, but realised I'd picked up white instead(!)

Note

Now, I do plan to refinish this wooden worktop, so I actually sanded it down, removing any old silicone here too.

Also, I purposely didn't oil the wood first, incase it reacted with the silicone and prevent it from sticking down.

And I can confirm that for £18, I no longer have a leaking bathroom sink drain!

More Narrowboat Posts

• Our buying a narrowboat experience
• DIY boat fender hangers
• Installing narrowboat window privacy film
• Changing a narrowboat mixer tap
• How we sold our first house and bought a narrowboat (and another house)
• Narrowboat hire for our honeymoon

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